Elevator systems are always being designed to move faster, smoother and more intelligently up and down an elevator shaft of a building. One area of recent intensive improvement has been in reducing horizontal vibrations.
A conventional elevator system has a car platform with a support frame which operates with guide rails arranged in the elevator shaft of the building, and a passive suspension system for controlling mechanical forces between the car platform, the supporting frame, and the guide rails as the elevator car moves up and down the elevator shaft. For example, the elevator car platform is typically attached to the support frame with hard rubber pads, and the supporting frame, in turn, moves along the guide rails supported by either wheels having stiff springs or sliding gibs at four attachment points. There is typically a limited amount of space between the supporting frame and the guide rails. Because of this soft springs cannot be used and any anomalies in the guide rails can cause significant vibration in the car platform. In addition, the ride quality is typically affected by low frequency mechanical forces produced by low frequency forces on the elevator such as forces produced by offset load or wind buffeting of the building or passenger motions in the car platform and high frequency forces produced between the frame and the guide rails as the elevator moves up and down the elevator shaft. The low frequency mechanical forces have high stiffness requirements, while the high frequency mechanical forces have low stiffness requirements.
One disadvantage of the elevator system having the passive suspension system are that stiff springs and guide rail anomalies combine to cause significant car platform vibration and that the ride quality is compromised due to the inherent trade-off between mitigation of low frequency forces versus the high frequency mechanical forces. Moreover, another disadvantage with the conventional elevator is that significant levels of acoustic noise are produced and transmitted to the elevator cab by the guide wheels as they move along guide rails.
These problems are overcome by an elevator systems having an active guidance system (hereinafter referred to as the "AG system") as described, inter alia, in European patent application No. 0 467 673 and U.S. Pat. Nos. 5,321,217; 5,304,751; 5,294,757; 5,308,938; 5,322,144. The AG system has an active suspension system for controlling mechanical forces between the supporting frame of the elevator/cab and the guide rails as the elevator moves up and down the elevator shaft. In the AG systems, the support frame has active roller guides, magnetic guide heads or other active horizontal suspensions which operate with the guide rails, and a controller for independently controlling one or more selected parameters indicative of horizontal vibrations or movements in a servo control loop as the elevator moves up and down within the elevator shaft.
However, the known AG systems utilize localized controllers which attempt to independently control the physical relationship between the guide heads, roller guides, slide guides, etc., and the guide rails in each axis of motion. These localized controllers do not share information. One disadvantage of an AG system having localized controllers is that forces which control one axis can have an adverse effect on other axes.
The proposed elevator AG system utilizes a coordinating controller which attempts to decouple the system dynamics by transforming the effective control into a global coordinate system aligned with the principle axis of the elevator car. By sharing information (sensing and actuation) from each guide head this system can minimize the amount of dynamic coupling (i.e., minimize the off-diagonal terms in the system plant transfer function) thereby allowing effective single-input/single-output (SISO) control logic to be developed for each axis of control in the new global coordinate system. This is an improvement over AG systems which use localized control whose performance is restricted by unmodeled and uncompensated dynamic interactions.